The invention relates generally to improvements in robotic systems performing automated manipulated functions on workpieces such as automotive vehicle bodies. More specifically, the invention pertains to robotic paint finishing of such objects in automatic paint finishing lines of high capacity.
Conventional robotic automotive paint finishing booths, such as that depicted in FIGS. 1a and 1b utilize multiple paint atomizers as well as robots or reciprocator machines in order to distribute paint across all required surfaces of the object passing through the paint application booth.
The paint application process can be performed either on a moving or stationary object, such as a car body. In either case, the object is indexed down the finishing line after the paint application process is complete. FIGS. 1a and 1b set forth a top and cross-sectional view, respectively, of a paint application zone 104 in a paint spray booth 100. Six robots 102a–f, three on each side of the paint application zone 104, each carry a paint application or distribution device 107a–f, such as a rotary bell, carried on a single manipulator arm or arm assembly 103a–f. Conventionally, an automotive chassis 106 is conveyed by a conveyor system 108 down the center of the spray booth through application zone 104 and is painted by the sets of three individual robots with single manipulator arms stationed on either side of the conveyor system 108.
Conventional paint robots 102a–f as shown in FIGS. 1a, 1b typically respectively consist of a base segment 105a–f which can be stationary or movable in the direction of conveyor system 108 and an arm assembly 103a–f comprising a vertical arm segment, a horizontal arm segment and a wrist segment holding the paint application device 107a–f. 
The term “arm”, as used herein, is intended to encompass either a manipulator arm composed of a single arm element or an assembly comprising a multi-segment arm, where pairs of the segments may be interconnected by joints as shown in FIGS. 1a, 1b. 
Such a prior art arrangement has the favorable features of repeatability of design, spare parts and maintenance; lower programming effort for identical robot units; and favorable downgrade arrangements should one of the robots fail. However, the prior art arrangement also presents important disadvantages. All robots are of the largest size required to paint the highest and the furthest portions of the object from the paint distribution devices, for example, the roof of the car body 106 shown in FIGS. 1a, 1b. Additionally, the maximum reach envelope of each robot 102 must be capable of covering both the lowest and the highest point of object 106. This, in turn, requires that all robots 102a-f be equipped with the largest required reach envelope.
An additional disadvantage of the prior art arrangement is that the combined effect of large envelope and high paint applicator relocation speed requires a sturdier robot to cope with the static and dynamic loads that it must handle which, in turn, results in higher total system cost. Also disadvantageous is the fact that the robots 102 require a relatively wide booth in order to paint vertical surfaces on object 106, due to the length of the manipulator arms of the robots. The robots 102 require space, either in front or at the back, in order to position the paint application device, such as an atomizer 107, at a suitable spraying distance in front of the surface to be painted.
Additionally, robots 102 often must be moved forward or backward along the line in order to paint the lower portions of part 106, such as a rocker panel, which requires a relatively longer spray booth paint application zone 104, along with an additional traveling axis (also known as the X-rail) being provided for robot movement longitudinally along application zone 104.
Finally, another disadvantage of the prior art arrangement is that at least two of the robots 102 perform very simple operations of reciprocating in the vertical surface of part 106. A much simpler machine than a full 7-axis robot can perform this operation.